Liquid crystal device and method for fabricating the same

ABSTRACT

A liquid crystal device includes a pair of electrode substrates opposing each other, a polymer wall, and a liquid crystal region surrounded by the polymer wall, the polymer wall and the liquid crystal region being sandwiched by the pair of electrode substrates. At least one of a concave portion and a convex portion is formed on a surface of at least one of the pair of electrode substrates facing the liquid crystal region, and liquid crystal molecules are oriented in the liquid crystal region axial-symmetrically around the vicinity of the at least one of concave portion and convex portion as an axis vertical to the electrode substrates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal device which can beused for flat displays for portable information terminals, personalcomputers, wordprocessors, amusement apparatuses, television sets, etc.viewed by a plurality of viewers, display boards employing a shuttereffect, windows, doors, walls, or the like, and a method for fabricatingthe same.

2. Description of the Related Art

As Liquid crystal devices such as liquid crystal display devicesemploying the electro-optic effect, the twisted nematic (TN) type, thesuper twisted nematic (STN) type, and the like using nematic liquidcrystal have already been commercialized. These types of liquid crystaldevices require polarizing plates and aligning treatment. These liquidcrystal devices, such as liquid crystal display devices, have a pretiltangle in an initial orientation state, so that liquid crystal moleculesraise in the direction of the pretilt angle when the liquid crystal cellis applied with a voltage, as shown in FIG. 22B. Accordingly, when sucha liquid crystal display device is viewed from different viewing anglesA and B, the apparent refractive index of the liquid crystal moleculesdiffers depending on the viewing angle, changing the contrast of thedisplay or even inverting the contrast at the gray scale display leveldepending on the viewing angle. This significantly lowers the displayquality.

On the other hand, some liquid crystal devices utilize scatteringphenomena of liquid crystal, and do not use polarizing plates. Thesedevices use a dynamic scattering (DS) effect and a phase change (PC)effect.

In recent years, a method for electrically controlling the transparentand opaque states of liquid crystal by using the birefringence of liquidcrystal has been proposed. This method requires neither polarizingplates nor aligning treatment. According to this method, basically, theordinary ray refractive index of liquid crystal molecules and therefractive index of a support medium are set identical. The transparentstate is presented when the liquid crystal molecules are aligned byapplying a voltage. The opaque state caused by light-scattering ispresented when the liquid crystal molecules are not aligned, i.e., whenno voltage is applied.

The above method is disclosed, for example, in Japanese Laid-OpenNational Patent Publication No. 58-501631 where liquid crystal iscontained in a polymer capsule, and in Japanese Laid-Open NationalPatent Publication No. 61-502128 where liquid crystal and a photocurableresin or a thermosetting resin are mixed and the resin in the mixture iscured to separate the liquid crystal from the resin, thereby formingliquid crystal droplets in the resin. The liquid crystal devicesobtained by these methods are called "polymer dispersed liquid crystaldisplay devices".

Moreover, methods for improving the viewing angle characteristic of aliquid crystal cell by employing polarizing plates are disclosed inJapanese Laid-Open Patent Publication Nos. 4-338923 and 4-212928, wherethe above-described polymer dispersed liquid crystal display device issandwiched between polarizing plates disposed to cross each other atright angles. This device greatly improves the viewing anglecharacteristic. However, since this device utilizes, in principle,depolarization caused by light scattering, the brightness of this typeof device is half as low as that obtained by a TN mode device, andtherefore the usability is low.

Further, another method for improving the viewing angle characteristicis disclosed in Japanese Laid-Open Patent Publication No. 5-27242, wherethe orientation of liquid crystal is disturbed by a polymer wall and aprotrusion so as to form randomly liquid crystal domains. In thismethod, however, since the domains are formed randomly and a polymermaterial is present in pixel portions, the light transmittance at thetime of no voltage application is lowered. Moreover, disclination linesrandomly arise at the boundary of the liquid crystal domains and do notdisappear even when a voltage is applied. This results in degradation ofthe black level at the time of voltage application. Due to the abovereasons, the contrast of this type of the liquid crystal device islowered.

Yet another method for improving the viewing angle characteristic isproposed by Japanese Laid-Open Patent Publication No. 6-301015 andJapanese Patent Application No. 5-199285 assigned to the same assigneeof the present application, where liquid crystal molecules are alignedaxial-symmetrically, for example, radially or concentrically(tangentially).

The above-described liquid crystal devices significantly improve theviewing angle characteristic, as described above. However, in theseliquid crystal devices, the orientation of the liquid crystal may bedisturbed due to undefined factors such as remainders of resist andscratches on the substrate. This causes the symmetry axis of theorientation of the liquid crystal molecules to incline or displace asshown in FIG. 23. This figure is a diagram of a liquid crystal deviceobserved with a polarizing microscope. In such a case, when the liquidcrystal device is viewed from different viewing angles, the area of aregion of which orientation corresponds to a certain viewing direction(a black region) in one pixel becomes greater compared with otherpixels. As a result, the average transmittance of the pixel differs fromthe transmittance of other pixels. This is observed by the viewer asroughness of display. Accordingly, in the above liquid crystal devices,the symmetry axis for the orientation of liquid crystal molecules shouldbe strictly controlled.

Moreover, it is necessary to stabilize the axial-symmetric orientationstate for easy fabrication of liquid crystal devices. Theaxial-symmetric orientation is mainly disturbed by the non-uniformity ofsurface free energy on the substrate.

SUMMARY OF THE INVENTION

The liquid crystal device of this invention includes a pair of electrodesubstrates opposing each other, a polymer wall, and a liquid crystalregion surrounded by the polymer wall, the polymer wall and the liquidcrystal region being sandwiched by the pair of electrode substrates. Atleast one of a concave portion and a convex portion is formed on asurface of at least one of the pair of electrode substrates facing theliquid crystal region, and liquid crystal molecules are oriented in theliquid crystal region axial-symmetrically around the vicinity of the atleast one of the concave portion and the convex portion as an axisvertical to the electrode substrates.

According to another aspect of the invention, a liquid crystal deviceincludes a pair of electrode substrates opposing each other, a polymerwall, and a liquid crystal region surrounded by the polymer wall, thepolymer wall and the liquid crystal region being sandwiched by the pairof electrode substrates. A column is formed on a surface of at least oneof the pair of electrode substrates facing the liquid crystal region,and liquid crystal molecules are oriented in the liquid crystal regionaxial-symmetrically around the vicinity of the column as an axisvertical to the electrode substrates.

According to still another aspect of the invention, a liquid crystaldevice includes a pair of electrode substrates opposing each other, apolymer wall, and a liquid crystal region surrounded by the polymerwall, the polymer wall and the liquid crystal region being sandwiched bythe pair of electrode substrates. At least one of a concave portion anda convex portion is formed on a surface of at least one of the pair ofelectrode substrates facing the liquid crystal region, and liquidcrystal molecules are oriented in the liquid crystal regionaxial-symmetrically around the vicinity of the at least one of theconcave portion and the convex portion as an axis vertical to theelectrode substrates. Further, a smooth resin portion is formed on asurface of one or both of the pair of electrode substrates facing theliquid crystal region.

According to still another aspect of the invention, the liquid crystaldevice includes a pair of electrode substrates opposing each other, apolymer wall, and a liquid crystal region surrounded by the polymerwall, the polymer wall and the liquid crystal region being sandwiched bythe pair of electrode substrates. A column is formed on a surface of atleast one of the pair of electrode substrates facing the liquid crystalregion, and liquid crystal molecules are oriented axial-symmetricallyaround the vicinity of the column as an axis vertical to the electrodesubstrates. Further, a smooth resin portion is formed on a surface ofone or both of the pair of electrode substrates facing the liquidcrystal region.

In one embodiment of the invention, the smoothed electrode substrateincludes a substrate for a matrix type LCD, a substrate provided with acolor filter, a substrate provided with active elements, and a substrateprovided with a striped electrode.

In another embodiment of the invention, a color filter is formed on atleast one of the pair of electrode substrates, and concaves betweencolor filter portions of the color filter corresponding to the liquidcrystal regions are filled with a resin forming the resin portions andsmoothed.

In still another embodiment of the invention, active driving elementsfor driving the liquid crystal by applying a driving voltage toelectrodes of the electrode substrates are formed on at least one of thepair of electrode substrates, and the active driving elements andwirings thereof are covered with a resin forming the resin portions andsmoothed.

In still anther embodiment of the invention, the at least one of theconcave portion and the convex portion are made of a film having avertical alignment property or a horizontal alignment property.

In still anther embodiment of the invention, the liquid crystal regionis composed of a plurality of liquid crystal domains dividing a pixel,and the polymer wall is formed at the periphery of each of the pluralityof liquid crystal domains.

In still another embodiment of the invention, a colored additive isincluded in the polymer wall.

In still anther embodiment of the invention, concaves and convexes areformed axial-symmetrically or continuously around the vicinity of asymmetry axis for the orientation of the liquid crystal molecules.

In still another embodiment of the invention, a region where thedistance between the electrodes of the pair of electrode substrates isdifferent from the distance in other regions exists in the vicinity ofthe symmetry axis for the orientation of the liquid crystal molecules.

In still anther embodiment of the invention, a first wall is formed on asurface of at least one of the pair of substrates facing the liquidcrystal region so as to surround the liquid crystal region or the liquidcrystal domain, and a height H of the first wall and a height h of theconvex portion have a relationship of H>h.

In still another embodiment of the invention, the at least one of theelectrode substrates has a color filter, the color filter including aplurality of color filter portions corresponding to a plurality ofpixels, and the concave portion is formed on a surface of each of thecolor filter portions facing the liquid crystal region.

In still another embodiment of the invention, the at least one of theelectrode substrates includes convex walls formed between the pluralityof color filter portions and an overcoat layer covering the plurality ofcolor filter portions and the convex walls.

In still another embodiment of the invention, the convex walls have alight shielding property.

According to still another aspect of the invention, a liquid crystaldevice includes a pair of electrode substrates opposing each other, apolymer wall, and a liquid crystal region surrounded by the polymerwall, the polymer wall and the liquid crystal region being sandwiched bythe pair of electrode substrates. An alignment film made of a polymerhaving axial-symmetric orientation axes is formed on a surface of atleast one of the pair of electrode substrates facing the liquid crystalregion, and liquid crystal molecules are oriented in the pixelaxial-symmetrically around the vicinity of at least one of a concaveportion and a convex portion as an axis vertical to the electrodesubstrates.

According to still another aspect of the invention, a method forfabricating a liquid crystal device, includes the steps of:

fabricating a cell by forming a first wall on at least one of a pair ofelectrode substrates, forming at least one of a concave portion and aconvex portion at a center portion of a region surrounded by the firstwall, or forming an alignment film having at least one of a concaveportion and a convex portion at the center portion of the regionsurrounded by the first wall, and disposing the pair of electrodesubstrates to oppose each other;

injecting a mixture including at least liquid crystal and a curableresin into the cell; and

phase-separating the liquid crystal from the curable resin by curing thecurable resin at a temperature equal to or more than a homogeneouslymiscible temperature of the mixture.

According to still another aspect of the invention, a method forfabricating a liquid crystal device, includes the steps of:

fabricating a cell by forming a first wall on at least one of a pair ofelectrode substrates, forming at least one of a concave portion and aconvex portion at a center portion of a region surrounded by the firstwall, or forming an alignment film having at least one of a concaveportion and a convex portion at the center portion of the regionsurrounded by the first wall, and then disposing the pair of electrodesubstrates to oppose each other;

injecting a mixture of at least liquid crystal and a curable resin intothe cell; and

phase-separating the liquid crystal from the curable resin by firstheating the mixture to a homogeneously miscible temperature of themixture and then gradually cooling the mixture, and curing the curableresin.

According to still another aspect of the invention, a method forfabricating a liquid crystal device, includes the steps of:

fabricating a cell by forming a first wall on at least one of a pair ofelectrode substrates and forming at least one of a concave portion and aconvex portion made of a film having a vertical alignment property or ahorizontal alignment property at a center portion of a region surroundedby the first wall, and disposing the pair of electrode substrates tooppose each other;

injecting a mixture of at least liquid crystal and a curable resin intothe cell; and

heating the mixture to a homogeneously miscible temperature of themixture, curing the curable resin by exposing to light, and thengradually cooling the mixture.

According to still another aspect of the invention, a method forfabricating a liquid crystal device, includes the steps of:

fabricating a cell by forming a first wall on at least one of a pair ofelectrode substrates, forming an alignment film having axial-symmetricorientation axes by phase-separating a mixed material containing two ormore different types of polymer materials in a region surrounded by thefirst wall, and then disposing the pair of electrode substrates tooppose each other;

injecting a mixture of at least liquid crystal and a curable resin intothe cell; and

curing the curable resin at a temperature equal to or more than ahomogeneously miscible temperature of the mixture and phase-separatingthe liquid crystal from the curable resin.

According to still another aspect of the invention, a method forfabricating a liquid crystal device, includes the steps of:

fabricating a cell by forming a first wall on at least one of a pair ofelectrode substrates, forming an alignment film having axial-symmetricorientation axes by phase-separating a mixed material containing two ormore different types of polymer materials in a region surrounded by thefirst wall, and then disposing the pair of electrode substrates tooppose each other;

injecting a mixture of at least liquid crystal and a curable resin intothe cell; and

phase-separating the liquid crystal from the curable resin by firstheating the mixture to a homogeneously miscible temperature of themixture and then gradually cooling the mixture, and curing the curableresin.

In one embodiment of the invention, the curable resin is cured while atleast one of a voltage and a magnetic field is applied to the cell.

In another embodiment of the invention, active driving elements fordriving the liquid crystal by applying a voltage to electrodes of theelectrode substrates are formed on one of the pair of electrodesubstrates, and a gate driving signal voltage applied to the activedriving elements at the curing of the curable resin is synchronous witha source driving signal voltage applied to the active driving elements,and the pulse width of the gate driving signal voltage is a half or lessof the cycle of the source driving signal voltage.

According to another aspect of the invention, a method for fabricating aliquid crystal device includes a pair of electrode substrates opposingeach other, a polymer wall, and a liquid crystal region surrounded bythe polymer wall, the polymer wall and the liquid crystal region beingsandwiched by the pair of electrode substrates, at least one of the pairof electrode substrates being fabricated by a method comprising thesteps of:

forming a plurality of color filter portions on a surface of thesubstrate;

forming convex walls between the color filter portions;

forming concave portions on the surface of the plurality of color filterportions facing the liquid crystal region by forming an overcoat layercovering the plurality of color filter portions and the convex walls.

In one embodiment of the invention, the step of forming the concaveportions comprises the steps of:

applying a resist covering the plurality of color filter portions; and

forming the convex walls between the plurality of color filter portionsby exposing the resist to light and developing.

According to the present invention, a concave portion and/or a convexportion or a column are formed on the surface of at least one of a pairof electrode substrates facing a display medium. When a mixturecontaining at least liquid crystal and a curable resin is injected intoa space between the pair of substrates and the liquid crystal and thecurable resin (polymer) are phase-separated, the liquid crystal appearsat the concave portion or a liquid crystal region develops surroundingthe convex portion. As a result, the liquid crystal molecules areoriented axial-symmetrically, for example, radially or concentrically,using the vicinity of the concave portion, the convex portion, or thecolumn as a symmetry axis vertical to the substrates. Accordingly, theposition of the symmetry axis can be controlled by controlling theformation of the concave portion and the convex portion, so as to obtaina uniform orientation of the liquid crystal. The "uniform orientation"as used herein refers to the state where the symmetry axis exists ineach pixel in the same positional relationship and liquid crystalmolecules are oriented axial-symmetrically with respect to the symmetryaxis.

Further, by smoothing the surface of the other electrode substratesfacing the substrate, on which the concave portion and/or the convexportion are formed, so as to eliminate a cause of disturbing theorientation of liquid crystal molecules in a liquid crystal droplet, theliquid crystal droplet can be aligned only based on the concave orconvex portion described above. For example, when a color filter, whichhas color filter portions each corresponding to a pixel, is disposed onone of the electrode substrates, liquid crystal appears at concavesformed between color filter portions of the color filter. This isbecause liquid crystal tends to be separated at portions having a largercell thickness. Therefore, the axially symmetrical orientation of theliquid crystal droplet is disturbed by the concaves between the colorfilter portions. This trouble can be overcome by filling the concaveswith a resin to smooth the surface. Thus, the liquid crystal appearsonly at the convex or concave portions formed on the substrate facingthe color filter portions. As another example, when active drivingelements are formed on one of the electrode substrates, many steps areformed on the surface by the multilayer structure of the active drivingelements and the wirings thereof. The axial-symmetric orientation of theliquid crystal molecules in the droplet may be disturbed by these steps.This trouble can also be overcome by filling the steps with a resin tosmooth the surface. Thus, the liquid crystal phase appears only at theconcave or convex portion described above.

The liquid crystal molecules can be aligned axial-symmetrically byforming a concave portion (of a conical shape, for example) on thesurface of each color filter portion facing the liquid crystal layercorresponding to each pixel. Such a concave portion can be formed byforming a convex wall between the adjacent color filter portions andthen forming an overcoat layer covering the color filter portions andthe convex walls. The convex walls can be provided with a lightshielding property by including a black dye and the like in the materialof the convex portion. The convex portion can be formed easily bylithography by use of a photosensitive material such as a resist.

The above concave portion and/or convex portion are preferably made of afilm or a material having a vertical alignment property so as to ensurethe stable control of the axis for the axial-symmetric orientation.

The liquid crystal region may be covered with a single liquid crystaldomain or a plurality of liquid crystal domains dividing one pixel. Thepolymer wall may be formed at the periphery of each liquid crystalregion or at the periphery of each liquid crystal domain so as tosurround the pixel or divide the pixel to form the liquid crystaldomains, respectively.

The disclination line can be less visible by coloring the polymer wallby use of an additive developing a color such as black.

Concaves and convexes may be formed axial-symmetrically and/orcontinuously around the symmetry axis of the orientation of the liquidcrystal molecules formed as described above. By this arrangement, thecenter or the vicinity of the center of the concaves and the convexescan be used as the axis for the axial-symmetric orientation so as torealize the orientation having the axis at the same position for all thepixels.

The above convex or concave portion may be formed on the electrode.Alternatively, the substrate itself may be deformed to have a concave ora convex and the electrode may be formed on the deformed substrate. Ineither case, the distance between the two electrodes on the pair ofsubstrates at the portion where the concave or convex is formed becomesdifferent from the other portions. An alignment film may also be formedon the deformed substrate having a concave or a convex to obtain analignment film with a concave or a convex. These are effective instabilizing the orientation of the liquid crystal molecules.

A first wall which has a different surface tension from the other regionmay be formed on the surface of at least one of the pair of substratesfacing the display medium. By forming the first wall, theaxial-symmetric orientation of the liquid crystal molecules can bestabilized without using a photoresist. In this case, if the height ofthe convex portion is larger than that of the first wall, a polymercolumn may be formed on the convex portion, resulting in disturbing theorientation of the liquid crystal molecules.

The mixture containing at least the liquid crystal and the curable resinmay be phase-separated by curing the curable resin at a temperatureequal to or more than the temperature at which they are homogeneouslymiscible with each other (hereinafter, such a temperature is referred toas a "homogeneously miscible temperature"). Alternatively, the mixturemay be heated to the homogeneously miscible temperature and thengradually cooled so as to allow the liquid crystal and the curable resinto be phase-separated and then the curable resin to be cured.

A voltage and/or a magnetic field may be applied to the cell at the timeof phase separation, so that the symmetry axis for the orientation ofthe liquid crystal molecules can be made vertical to the substrates.

An alignment film made of a polymer film having axial-symmetricorientation axes is formed on the surface of at least one of the pair ofsubstrates facing the display medium. The orientation axes of the liquidcrystal molecules are substantially identical to the orientation axes ofthe polymer of the alignment film. Accordingly, the liquid crystal canbe aligned axial-symmetrically, for example, radially or concentrically,around the axis vertical to the substrates as the symmetry axis.

The above alignment film can be formed by phase-separating a mixedmaterial containing two or more different types of polymer materials inthe region surrounded by the first wall.

Further, the signal voltage for driving the gate of the active drivingelement may be synchronous with the signal voltage for driving thesource thereof, the pulse width of the former may be a half or less ofthe cycle of the latter, and the resin may be cured while the voltage isapplied. Accordingly, the potential difference between the pixelelectrode and the gate line formed on the same substrate is decreased,and such a trouble that the axially symmetrical orientation of theliquid crystal molecules is disturbed due to the potential at the gateline can be overcome.

Thus, the invention described herein makes possible the advantages of(1) providing a liquid crystal device capable of improving the viewingangle dependency by realizing the axial-symmetric orientation of liquidcrystal molecules and capable of reducing the roughness of display bycontrolling the axis for the axial-symmetric orientation, and (2)providing a method for fabricating such a liquid crystal device.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a liquid crystal display deviceaccording to the present invention.

FIG. 2 is a diagram of a liquid crystal display device according to thepresent invention observed with a polarizing microscope.

FIG. 3 is a diagram of another liquid crystal display device accordingto the present invention observed with a polarizing microscope.

FIGS. 4A and 4B are sectional views showing other liquid crystal displaydevices according to the present invention.

FIG. 5 is a sectional view of the liquid crystal cell of Example 4.

FIG. 6 is a sectional view of yet another liquid crystal display deviceaccording to the present invention.

FIG. 7 is a sectional view of yet another liquid crystal display deviceaccording to the present invention.

FIG. 8 is a sectional view of yet another liquid crystal display deviceaccording to the present invention.

FIG. 9 is a sectional view of yet another liquid crystal display deviceaccording to the present invention.

FIGS. 10A and 10B are sectional views of other liquid crystal displaydevices according to the present invention.

FIG. 11 is a sectional view of the liquid crystal cell of Example 1.

FIG. 12 is a sectional view of the liquid crystal cell of Example 2.

FIGS. 13A to 13C are sectional views showing the fabrication process ofone substrate of the liquid crystal display device of FIG. 3.

FIG. 14A is a plan view showing the liquid crystal cell of Example 6.

FIGS. 14B to 14D are sectional views of the fabrication process of aliquid crystal cell according to the present invention.

FIG. 15 is a schematic view showing the separation of the liquid crystalphase from the mixture.

FIGS. 16A to 16F show the electro-optic characteristics of the liquidcrystal display device of Example 1.

FIGS. 17A to 17F show the electro-optic characteristics of the liquidcrystal display device of Comparative Example 1.

FIG. 18 is a sectional view of the liquid crystal cell of Example 3.

FIG. 19 is a plan view of the liquid crystal cell of Example 5.

FIG. 20 is a sectional view of the liquid crystal cell of ComparativeExample 2.

FIGS. 21A and 21B are diagrams of the liquid crystal cell of ComparativeExample 2 observed with a polarizing microscope.

FIGS. 22A to 22C and FIGS. 22D to 22F are diagrams for explaining thechange in the contrast depending on the viewing angle for liquid crystaldisplay devices in a wide viewing angle mode and a TN mode,respectively,

FIG. 23 is a diagram for explaining the roughness of a display due tothe displacement of the orientation axis of liquid crystal molecules.

FIG. 24 is a plan view showing a resist pattern formed on a color filtersubstrate according to the present invention.

FIG. 25 is a sectional view taken along line C-C' of FIG. 24.

FIG. 26 is a sectional view showing an axial-symmetric orientation modelat the mode according to the present invention.

FIG. 27 is a plan view showing a resist pattern formed on a substratehaving active elements according to the present invention.

FIG. 28 is a sectional view taken along line A-A' of FIG. 27.

FIG. 29 is a sectional view of the liquid crystal cell of Example 7.

FIG. 30 is a diagram of the liquid crystal cell of Example 7 observedwith the polarizing microscope.

FIG. 31 is a sectional view of the liquid crystal cell of Example 9.

FIG. 32 is a timing diagram of a source signal, a gate signal, and acounter voltage to be applied to pixel electrodes of the liquid crystaldisplay device of Example 10.

FIGS. 33A to 33E are sectional views showing the steps for fabricating acolor filter substrate according to the present invention.

FIG. 34 is a sectional view of a color filter substrate of ComparativeExample 3 where the surface is smoothed.

FIG. 35 is a sectional view of a conventional color filter ofComparative Example 4.

FIGS. 36A to 36C schematically show the position of the formation of aliquid crystal region in the fabrication process of the liquid crystalcells of Example 11 and Comparative Examples 3 and 4.

FIGS. 37A to 37C show diagrams of the liquid crystal cells of Example 11and Comparative Examples 3 and 4 observed with the polarizingmicroscope.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described by way of examples as follows.

FIG. 1 is a sectional view showing one pixel portion of a liquid crystaldisplay device according to the present invention.

Referring to FIG. 1, a pixel electrode 3 made of indium tin oxide (ITO)or the like is formed on a transparent substrate 1 made of glass or thelike. A convex portion 4 made of a resist or the like is formed at thecenter of the pixel electrode 3, and a first wall 5 made of a resist orthe like is formed to surround the pixel. A counter electrode 6 made ofITO or the like is formed on another transparent substrate 2 made ofglass and the like.

As shown in FIG. 2, a liquid crystal region 8 surrounded by a polymerwall 7 is formed between the transparent substrates 1 and 2 for eachpixel. Liquid crystal molecules in the liquid crystal region 8 (in eachpixel) are aligned radially around the vicinity of the convex portion 4as the axis vertical to the substrates 1 and 2, achieving a uniformorientation state.

As described above, the liquid crystal molecules are intentionallyaligned around the convex portion 4 axial-symmetrically (for example,radially, concentrically, and swirlingly) in the liquid crystal region8. Also, the liquid crystal region 8 is substantially a mono-domainregion. With this arrangement, the viewing angle characteristic can beimproved and the roughness of display, especially at the gray scalelevel, can be reduced.

(Orientation state of liquid crystal molecules in the domain)

When the liquid crystal display device of this example is observed witha polarizing microscope, a cross-shaped extinction pattern 11 isobserved in the liquid crystal region 8 surrounded by the polymer wall 7in a direction of the polarizing axis of polarizing plates, as shown inFIG. 2. This indicates that the liquid crystal molecules are alignedaround a center disclination point 12 at the center of the liquidcrystal region 8 axial-symmetrically (for example, radially,concentrically, and swirlingly) and that the liquid crystal region 8 isa mono-domain region.

In the liquid crystal display device in the above orientation state, adisclination line (not shown in FIG. 2) is formed outside a liquidcrystal domain 14 at the time of voltage application, but will never beformed inside the liquid crystal domain 14. Accordingly, it is possibleto intentionally form a disclination line outside the pixel. Further,the disclination line or the disclination point may be formed under alight-shielding layer so as to improve the black level of the liquidcrystal display device and thereby to improve the contrast of thedisplay. In this case, the disclination line may be made less visible byadding an additive developing a color (black, for example) to thematerial of the polymer wall 7, or to the material of the convex portion4 and the first wall 5. Alternatively, an orientation state where nodisclination line arises can be obtained by adding a liquid crystallinepolymerizable material to the polymer wall 7.

When a display voltage is applied to the liquid crystal device havingthe above orientation state, liquid crystal molecules 9 rise so as to bevertical to the substrates 1 and 2, as shown in FIGS. 22A to 22C, forexample. At this time, the liquid crystal molecules 9 rise at therespective positions of the initial radial or concentric orientation.Accordingly, the apparent refractive indexes viewed in variousdirections are made uniform, and thus the viewing angle characteristicof the liquid crystal device can be improved.

(The number of domains in one pixel)

The number of domains in each pixel is preferably as small as possible.If a number of domains exist in one pixel, a disclination line arises ateach boundary of the domains, causing a degradation in the black levelof the display. It is preferable, therefore, that the pixel 13 iscovered by a single domain where liquid crystal molecules are alignedaxial-symmetrically in the liquid crystal region 8. With thisarrangement, since the disclination line is formed outside the domain atthe time of voltage application, the disclination line seldom intrudesinside the pixel 13.

In the case where the pixel 13 is rectangular, as shown in FIG. 3, theliquid crystal region 8 may have two or more domains 14 each havingliquid crystal molecules aligned axial-symmetrically. Such a liquidcrystal display device can also have the same excellent viewing anglecharacteristic as the liquid crystal display device having themono-domain liquid crystal region 8 as shown in FIG. 2. In the case ofthe liquid crystal display device shown in FIG. 3, the rectangular pixel13 may be divided into two by forming a wall like the polymer wall 7 andthe first wall 5 therebetween.

Further, in the liquid crystal display device shown in FIG. 3, thedirection of the disclination line 112 formed at the boundary of thedomains 14a and 14b in the pixel 13 may be made identical to thepolarizing axis of the polarizing plates, so that the disclination linecan be less visible at the time of voltage application.

Alternatively, it may be possible to form a black mask (BM) within apixel so as to hide the disclination line formed at the boundary of thedomains 14a and 14b in the pixel 13.

When the pixel is divided into a plurality of liquid crystal regions 8,or liquid crystal domains 14 as described above, it is required to alignthe orientation axis of the liquid crystal molecules in each liquidcrystal region 8 or liquid crystal domain 14.

(Method 1 for uniformly aligning liquid crystal moleculesaxial-symmetrically)

By forming a concave or convex portion or both thereof on at least oneof the pair of substrates, the liquid crystal molecules can be alignedaxial-symmetrically and the position of the symmetry axis is controlled.

According to this method, the first wall 5 is first formed bypatterning, and a concave or convex portion or both thereof is formed atsubstantially the center of a region surrounded by the first wall so asto form a portion having a different cell gap in the region. A mixturecontaining at least liquid crystal and a curable resin is injected intothe cell. When there exists a portion having a cell gap different fromthat of the other portions (excluding the first wall 5 surrounding thepixel), which is to serve as the symmetry axis in the pixel, the liquidcrystal and the curable resin (or polymer) are phase-separated toseparate the liquid crystal from the curable resin by a polymerizationreaction or temperature drop. How the liquid crystal is separateddiffers depending on the cases described below.

(1) In the case where the cell gap of the portion which serves as thesymmetry axis in the pixel at phase separation is small (when the convexportion is formed):

When the liquid crystal and the curable resin (or polymer) arephase-separated by a polymerization reaction or temperature drop, theconvex portion 4 on the substrate 1 as shown in FIG. 1 serves as anucleus for the separation of the liquid crystal, and the liquid crystalregion 8 develops surrounding the vicinity of the convex portion 8. As aresult, the liquid crystal molecules are aligned radially orconcentrically around the axis vertical to the substrates, so as toobtain the axial-symmetric orientation of the liquid crystal molecules.Simultaneously, the symmetry axis and the convex portion 4 can be madeidentical. This indicates that the position of the symmetry axis for thealignment of the liquid crystal molecules can be controlled bycontrolling the position of the convex portion 4, and that the liquidcrystal molecules can be aligned axial-symmetrically in the pixel.

The height of the convex portion 4 is preferably a half or less of thecell gap and smaller than the height of the first wall 5 formed outsidethe pixel 13 to surround the pixel region 8. If the convex portion 4 istoo high, a polymer pillar is formed on the convex portion 4. If thepolymer pillar is too high, the orientation state may be disturbed bythe polymer pillar.

The convex portion 4 should have a size appropriate to serve as thenucleus for the separation of the liquid crystal. The size is preferablyas small as possible. For example, it is 30 μm or less. If the convexportion 4 is too large, a polymer pillar is formed on the convex portion4. This results in voltage drop which is a cause of the reduction of thecontrast.

The convex portion 4 may be made of organic materials such as a resistand inorganic materials such as SiO₂, Al₂ O₃, and ITO, though notspecified in the present invention. When a resist material is used, theconvex portion 4 can be easily formed. When ITO which is transparent andconductive is used, as shown in FIGS. 4A and 4B, the convex portion canbe formed by forming the pixel electrode 3, made of ITO, over thesubstrate 1 on which the convex portion 4 has already been formed.Alternatively, as shown in FIG. 5, an alignment film 16 may be formedover the substrate 1 on which the convex portion 4 has already beenformed. In order to place such a convex portion (the convex portion 4covered with the pixel electrode or the alignment film) at the center ofthe axis for the alignment of the liquid crystal, it is preferable touse a material having a vertical alignment property. A resist materialwith F-based or Si-based additives added thereto, for example, can beused as such a material. In particular, a material having a surface freeenergy of 35 mN/m or less is preferable. Further, the orientationstability can be increased in some cases when the first wall 5 formedsurrounding the pixel and the convex portion are made of differentmaterials.

The convex portion 4 may have a shape of a circle, a square, arectangle, an oval, a star, a cross, or the like, though the shape isnot specified in the present invention. The convex portion 4 does notnecessarily have the same size in the vertical direction, but may betapered as shown in FIG. 6.

(2) In the case where the cell gap of the portion which serves as thesymmetry axis in the pixel at phase separation is large (when a concaveportion is formed):

When the liquid crystal and the curable resin (or polymer) arephase-separated by polymerization reaction or temperature drop(especially, by temperature drop), if a concave portion 15 is formed onthe substrate 1 as shown in FIG. 7, the liquid crystal phase-separatedfrom the curable resin forms a sphere having the minimum surface tensionat the concave portion 15 and is stabilized. As a result, the liquidcrystal appears at the concave portion 15 and the liquid crystal region8 develops surrounding the concave portion 15. Accordingly, the liquidcrystal molecules are aligned radially or concentrically around an axisvertical to the substrates, so as to obtain the axial-symmetricorientation of the liquid crystal molecules axial-symmetrically.Simultaneously, the symmetry axis and the concave portion 15 can be madeidentical. This indicates that the position of the symmetry axis for thealignment of the liquid crystal molecules can be controlled bycontrolling the position of the concave portion 15, and that the liquidcrystal can be aligned axial-symmetrically in the pixel.

The depth of the concave portion 15 is not specified in the presentinvention. However, when an organic material such as a resist 20 isused, the depth is preferably as small as possible because the smallerthe depth, the smaller the voltage drop which may cause lowering of thecontrast.

The size of the concave portion 15 is preferably large. However, to someextent, the size depends on the size of the pixel. Preferably, it isapproximately 40% of the area of the pixel.

The concave portion 15 may be made of an organic material, such as aresist 20, or an inorganic material such as SiO₂, Al₂ O₃, and ITO,though not specified in the present invention.

The concave portion 15 may have a shape of a circle, a square, arectangle, an oval, a star, a cross, or the like, though the shape isnot specified in the present invention. The concave portion 15 does notnecessarily have the same size in the vertical direction, but may betapered as shown in FIG. 8.

(3) In the case where both portions having a large cell gap and a smallcell gap are formed in the pixel (when both the concave and convexportions are formed):

When the liquid crystal and the curable resin (or polymer) arephase-separated by polymerization reaction or temperature drop, if boththe convex portion 4 and the concave portion 15 exist on the substrate1, the liquid crystal is separated at the concave portion 15 and theliquid crystal region 8 develops surrounding the convex portion 4 at thecenter of the pixel. Accordingly, by using the convex portion 4 as thesymmetry axis, the position of symmetry axis can be fixed for all thepixels, and thus the roughness of display can be reduced.

The convex and concave portions may be formed axial-symmetrically asshown in FIG. 9 or formed continuously as shown in FIG. 5.

The heights of the surfaces of the concave portion 15 and the convexportion 4 may be the same as that of the flat smooth surface, or theymay be different.

(4) In the case where the convex portion and/or concave portion areformed on the two substrates:

In the above cases (1) to (3), at least the concave portion 15 or theconvex portion 4, among the concave portion 15, the convex porion 4, andthe first wall 5, is formed on one of the pair of substrates. However,as shown in FIGS. 10A and 10B, the first wall 5 may be formed on thesubstrate 1, while the concave portion 15 or the convex portion 4 may beformed on the substrate 2 or on both substrates 1 and 2.

When at least one of the concave portion 15 and the convex portion 4 isformed on the substrate 1, an alignment film 17 may be formed on theother substrate, i.e., the counter substrate 2, as shown in FIGS. 5, 11,and 12. The alignment film 17 on the counter substrate 2 serves tosmooth a roughness on the counter substrate 2 or a passivation film (notshown) or make the surface energy uniform. Thus, at the phase-separationof the liquid crystal from the curable resin (or polymer), the liquidcrystal is prevented from separating at positions other than theabove-described concave portion and convex portion.

(5) In the case where a color filter is formed on the counter substrate:

The case where a color filter having a plurality of color filterportions each corresponding to a pixel is formed on the surface of thecounter substrate opposing the substrate on which the concave or convexportion is formed will be described. The color filter has concaveportions between adjacent filter portions corresponding to pixels. Atthe phase-separation of the liquid crystal from the curable resin (orpolymer), the liquid crystal separates at portions having a large cellthickness as described hereinbefore. Accordingly, the liquid crystaltends to separate at the concaves formed between adjacent filterportions, and therefore the axial-symmetric orientation of the liquidcrystal molecules in the droplet cannot be obtained. This problem can beovercome by filling these concaves with a resist resin to smooth thesurface of the color filter. Thus, since the cause of disturbance of theorientation of the liquid crystal molecules in the droplet can beeliminated, it is possible for the liquid crystal to appear only at theconcave portion or the convex portion formed on the substrate opposingthe color filter at the phase-separation of the liquid crystal from thecurable resin (or polymer).

(6) In the case where active driving elements are formed on the countersubstrate:

The case where active driving elements are formed on the smoothedelectrode substrate will be described. Since the active driving elementsand wirings thereof are multi-layered, many steps are formed. Thesesteps may disturb the axial-symmetric orientation of the liquid crystalmolecules. However, this problem can be overcome by filling the stepswith a resin to smooth the surface. Thus, it is possible for the liquidcrystal to appear only at the concave portion or the convex portion.

(Method for forming the concave portion, the convex portion, and thefirst wall)

The concave portion, the convex portion, and the first wall can beformed by the following methods.

(1) Using resist material:

The case where the substrate 1 having the convex portion 4 as shown inFIG. 1 will be described with reference to FIGS. 13A to 13C. First, aresist is applied to the substrate 1 shown in FIG. 13A and exposed tolight and developed to form the convex portion 4 at the center of thepixel as shown in FIG. 13B. Then, another resist is applied, exposed tolight, and developed to form the first wall 5 surrounding the pixel asshown in FIG. 13C. The convex portion 4 and the first wall 5 may be madeof the same material. The same process can be employed for the formationof the concave portion.

A material for an alignment film or a resist material may be applied tothe substrate 1 after the formation of the first wall 5 and solidified.The resultant alignment film or the resist has a thicker portion in thevicinity of the first wall 5. As a result, as shown in FIG. 10B, aconical concave portion 15 is obtained which is deepest at the center ofthe pixel and becomes increasingly shallower as it approaches the firstwall 5.

(2) Processing the substrate itself:

When a plastic substrate is employed, it is possible to roughen thesubstrate itself by embossing or the like so as to form the concaveportion, the convex portion, or the first wall. A transparent electrodeor an alignment film may be formed on the substrate having the concaveportion or the convex portion, as shown in FIGS. 4A, 4B, and 5.

(3) Using inorganic material:

An inorganic material such as SiO₂, Al₂ O₃, and ITO is deposited on thesubstrate and patterned by use of a mask, so as to form the concaveportion, the convex portion, or the first wall.

(Method for forming the substrate having a color filter opposing thesubstrate having the concave or convex portion)

FIG. 24 is a plan view showing a resist pattern formed on the substrateon which the color filter is formed (hereinafter, such a substrate isreferred to as the color filter substrate) according to the presentinvention. FIG. 25 is a sectional view taken along line C-C' of FIG. 24.Referring to FIGS. 24 and 25, a material for a light shielding film 32is deposited on a glass substrate 31 and patterned so as to etch thematerial on portions corresponding to pixel regions, thereby forminglight transmitting portions. The other portions of the material which donot correspond to the pixel regions are not etched to form the lightshielding films 32. R, G, and B color filter portions 33 are then formedon the light transmitting portions. A resist resin is applied to thecolor filter substrate having the color filter portions 33 and theresist resin deposited on the color filter portions 33 are removed, soas to form resist resin portions 34 on the respective light shieldingfilms 32. In this way, the concaves between the adjacent color filterportions 33 can be filled with the resist resin portions 34 to smooththe surface of the color filter substrate. By this smoothing, the causeof disturbance of the axial-symmetric orientation of the liquid crystalmolecules in the droplet can be eliminated, and the liquid crystal canbe separated only at the concave or convex portion disposed on theopposing substrate.

(Material for the concave portion and/or convex portion)

A general photoresist material can be used as the resist material. Sincethe concave portion 15, the convex portion 4, and the first wall 5remain in the cell, it is preferable to use photosensitive polyimidewhich is excellent in thermal resistance. When a resist material isused, liquid crystal material tends to remain on the resist in the pixel(the periphery 20 of the concave portion 15 and the convex portion 4 inFIG. 9, for example), thereby lowering the contrast. Accordingly, aresist material having the light shielding property is preferable. Forexample, a color resist where a coloring matter is contained in a resistmaterial can be used.

It is observed from an axial-symmetric orientation model shown in FIG.26 that liquid crystal molecules 42 are oriented vertically in thevicinity of a symmetry axis 41 for axial symmetry. From this fact, inorder to facilitate the axial-symmetric orientation of liquid crystalmolecules, it is suggested that the liquid crystal molecules in thevicinity of the center of the pixel should be positively aligned in thevertical direction. It is then suggested that the concave portion 15 orthe convex portion 4 should be formed of a material having a verticalalignment property. As such a material having the vertical alignmentproperty, an organic material such as polyimide having the verticalalignment property provided with photosensitivity, an obliquelydeposited inorganic film made of a material such as SiO₂, and the likecan be used. Alternatively, a vertical alignment film may be firstformed on the substrate and then covered with a horizontal alignmentfilm except for the portion corresponding to the center of the pixel,thus exposing the vertical alignment film only at the center of thepixel.

(Method 2 for uniformly aligning liquid crystal moleculesaxial-symmetrically)

An alignment film 16a made of a polymer having axial-symmetricorientation axes as shown in FIG. 14A may be formed on one of thesubstrates. With this arrangement, the liquid crystal molecules can bealigned axial-symmetrically with the orientation axes of the liquidcrystal molecules being substantially identical to the orientation axesof the alignment film 16a.

(Method for forming the axial-symmetric alignment film)

Referring to FIGS. 14B to 14D, after formation of the first wall 5, amixed material containing two different polymer materials is applied toa substrate 1a. Two polymer materials in the mixture are thenphase-separated axial-symmetrically, i.e., radially, concentrically, orthe like, so as to form the alignment film having the axial-symmetricorientation axes.

A cell is formed by use of the substrate 1a having the axial-symmetricalignment film, and a mixture of liquid crystal and a curable resin (orpolymer) is injected into the cell. Then, the mixture is subjected topolymerization or a temperature drop so as to phase-separate the liquidcrystal from the curable resin. As a result, the liquid crystalmolecules are aligned axial-symmetrically, with the orientation axes ofthe liquid crystal molecules being substantially identical to theorientation axes of the alignment film 16a.

(Method for forming the polymer wall)

The liquid crystal region surrounded by the polymer wall is formed inthe following manner:

(1) A mixture containing at least liquid crystal and a curable resin isinjected into the cell and cured at a temperature exceeding thehomogeneously miscible temperature of the mixture. Then, the liquidcrystal and the curable resin (polymer) are phase-separated, so as toform the liquid crystal region surrounded by the polymer wall.

(2) A mixture containing at least liquid crystal and a curable resin isinjected into the cell. The mixture is heated to or above thehomogeneously miscible temperature of the mixture and then graduallycooled, so as to phase-separate the liquid crystal from the curableresin. Thereafter, the curable resin is cured so as to form the liquidcrystal region surrounded by the polymer wall.

In the above methods (1) and (2), if a photocurable resin is used, theresin can be cured by irradiation with ultraviolet light (or visiblelight).

In either case, since the concave portion, the convex portion, or thealignment film has been formed, the positions where the liquid crystalappears and the positions where the liquid crystal region and thepolymer wall are formed can be controlled without the necessity ofproducing an irradiation intensity distribution by a photomask.

(Method for controlling the alignment by polymer material)

(1) Addition of polymerizable liquid crystalline material:

In order to effectively align liquid crystal molecules in an orientationdirection at the time of voltage application, it is preferable to add apolymerizable liquid crystalline material such as a liquid crystallinephotocurable resin which includes a functional group exhibiting theliquid crystallinity or a similar functional group in a molecule to themixture of the liquid crystal and the curable resin. Moreover, when theliquid crystal in the mixture is phase-separated from the curable resinin the cell, the curable resin may be formed, in some cases, on anisland such as the convex portion made of a material having the verticalalignment property, blocking the effect of the vertical alignmentproperty. Therefore, it is preferable to add a curable resin having afunctional group which is likely to exhibit liquid crystallinity in thecurable resin so that the vertical alignment property of the island canbe transmitted to the liquid crystal phase even if the curable resin isformed on the island.

(2) Method for applying a voltage or a magnetic field at the time ofphase separation

It is important that the axial-symmetric orientation of liquid crystalmolecules is formed within the pixel, and the symmetry axis of theorientation should not be displaced so widely with respect to thesubstrate. According to the examination by the inventors, when a voltageand/or a magnetic field are applied to the mixture containing at leastthe liquid crystal and the curable resin (or polymer) at the time ofphase separation of the liquid crystal from the curable resin, it ispossible to fix the axis for the axial-symmetric orientation of theliquid crystal molecules in the liquid crystal region in the verticaldirection to the substrates for all the pixels. This phenomenon ispreferable because, by using the island having the vertical alignmentproperty such as the convex portion made of a material having thevertical alignment property for aligning the liquid crystal molecules,it is ensured that the axis for the axial-symmetric orientation can becontrolled more stably. The application of a voltage and/or a magneticfield is especially effective when the liquid crystal is in a smalldroplet state appearing from a uniform phase 19 as shown in FIG. 15.Therefore, the voltage and/or the magnetic field may be weakened beforethe liquid crystal region 8 expands to cover the entire pixel. Themagnitude of the voltage and the magnetic field should be greater than athreshold of the liquid crystal (a value evaluated by the TN cell) andmay be periodically changed.

Next, the case where active elements such as thin film transistors(TFTs) are formed on the substrate will be described.

FIG. 27 is a plan view of a substrate having active elements accordingto the present invention. FIG. 28 is a sectional view taken along lineA-A' of FIG. 27.

Referring to FIGS. 27 and 28, each pixel electrode is connected with adrain electrode of a TFT 43 as the active driving element. In order toapply a voltage to the pixel electrode, therefore, an appropriatevoltage should be applied to a gate electrode connected with a gate line44 so as to switch on the connection between a source line 45 and thepixel electrode, i.e., the connection between a source electrode and thedrain electrode of the TFT 43. Accordingly, when the mixture of theliquid crystal and the curable resin is phase-separated while applying avoltage to the mixture, the axial-symmetric orientation of the liquidcrystal molecules is disturbed due to a potential at the gate line 44because a potential difference is generated between the pixel electrode(drain electrode) and the gate line 44 formed on the same substrate.

The inventors have found that the above trouble of disturbing theaxial-symmetric orientation of the liquid crystal molecules can beovercome by appropriately controlling the timing and the time of theapplication of a voltage to the gate electrode, and the magnitude of thevoltage as described below.

In order to minimize the potential difference between the pixelelectrode and the gate line 44 formed on the same substrate, the voltageapplied to the pixel electrode of the cell should be such that, at thecuring of the curable resin, the signal voltage for driving the gateelectrode of the active driving element is synchronous with the signalvoltage for driving the source electrode of the active driving elementand that the pulse width of the former is a half or less of the cycle ofthe latter.

(Curable resin)

A photocurable resin and the like may be used as the curable resin forthe present invention. Examples of the photocurable resin include anacrylic acid and acrylates having a long-chain alkyl group with three ormore carbon atoms or having a benzene ring: more specifically, includeisobuthyl acrylate, stearyl acrylate, lauryl acrylate, isoamyl acrylate,n-buthylmethacrylate, n-laurylmethacrylate, tridecylmethacrylate,2-ethylhexylacrylate, n-stearylmethacrylate, cyclohexylmethacrylate,benzylmethacrylate, 2-phenoxyethylmethacrylate, isobornylacrylate, andisobornylmethacrylate. Further, in order to increase the physicalstrength of the polymer, a multi-functional resin having two or morefunctional groups is preferable. Examples of such a resin includebisphenol A dimethacrylate, bisphenol A diacrylate,1,4-butanedioldimethacrylate, 1,6-hexanedioldimethacrylate,trimethylolpropanetrimethacrylate, trimethylolpropanetriacrylate,tetramethylolmethanetetraacrylate, neopentyldiacrylate, and R-684.Further, in order to clearly phase-separate the liquid crystal from thecurable resin, resins obtained by halogenating, especially chlorinatingor fluorinating the above monomers, are more preferable. Examples ofsuch resins include 2,2,3,4,4,4-hexafluorobuthylmethacrylate,2,2,3,4,4,4-hexachlorobuthylmethacrylate,2,2,3,3-tetrafluoropropylmethacrylate,2,2,3,3tetrafluoropropylmethacrylate, parfluorooctylethylmethacrylate,parchloroocrylethylmethacrylate, parfluoroocthylethylacrylate, andparchlorooctylethylacrylate.

(Photopolymerization retarder)

It is preferable to add a compound retarding the polymerization otherthan the curable resin to the mixture so as to enlarge the liquidcrystal droplet, i.e., the liquid crystal region 8. Such a compound is,for example, a monomer or a compound which can stabilize a radical by aresonance effect after the production of the radical. For example,styrene, derivatives of styrene such as p-chlorostyrene,p-phenylstyrene, and p-methylstyrene, and a polymerization inhibitorsuch as nitrobenzene can be used.

(Photopolymerization initiator)

The mixture may also contain a photopolymerization initiator. Examplesof such an initiator include Irgacure 184, 651, 907 (manufactured byChiba Geigy), and Darocure 1173, 1116, 2956 (manufactured by E. Merck).A sensitizer which allows for the polymerization with visible light mayalso be added to the mixture to improve the retention.

The amount of the polymerization initiator added to the mixture is notspecified in the present invention because it differs depending on thereactivity of each compound. It is preferable, however, in the range of0.01% to 5% of the mixture of the liquid crystal and the curable resin(including the polymerizable liquid crystalline material to be describedlater). If the amount is less than 0.01%, the polymerization is notsufficient. If it is more than 5%, the phase separation of the liquidcrystal from the polymer occurs so fast that the control of the phaseseparation is difficult. The resultant liquid crystal droplet is small,and this increases the driving voltage and decreases the control of thealignment of the liquid crystal on the substrate. Further, the liquidcrystal region with the pixel becomes smaller, and, when the irradiationintensity distribution is produced by use of a photomask, the liquidcrystal droplet is formed in the light shielding portion (outside thepixel). This lowers the contrast of the display.

(Liquid crystal material)

An organic mixture exhibiting a liquid crystalline state at and around anormal temperature is used as the liquid crystal of the presentinvention. This includes nematic liquid crystal (liquid crystal for2-frequency driving; including liquid crystal of Δε<0), cholestericliquid crystal (in some cases exhibiting a selective reflectioncharacteristic against visible light), smectic liquid crystal,ferroelectric liquid crystal, and discotic liquid crystal. These typesof liquid crystal may be used in combination. The nematic liquid crystalwith the cholesteric liquid crystal (a chiral agent) added thereto ispreferable from the characteristic point of view.

Further, a liquid crystal material having excellent chemical reactionresistivity is preferable because the processing includes thephotopolymerization. Examples of such a liquid crystal material includeZLI-4801-000, ZLI-4801-001, ZLI-4792, and ZLI-4427 (manufactured byMerck).

(Polymerizable liquid crystalline material)

A liquid crystalline compound having a polymerizable functional group(referred to as the polymerizable liquid crystalline material; thismaterial itself does not need to exhibit the liquid crystallinity) maybe added to the mixture of the liquid crystal and the curable resin. Bythis addition, polymers in the polymer wall can serve to align theorientation direction of the liquid crystal molecules effectively at thetime of voltage application. Also, the disclination line arising at theperiphery of the liquid crystal region can be suppressed.

Preferably, the selected liquid crystal and polymerizable liquidcrystalline material resemble each other in the portions exhibiting theliquid crystallinity. In particular, when the liquid crystal is an F orCl based material which shows a distinct chemical property, thepolymerizable liquid crystalline material is preferably an F or Cl groupmaterial.

A compound expressed by formula (1) below is usable as the polymerizableliquid crystalline material.

    A-B-LC                                                     (1)

wherein A denotes a polymerizable functional group, for example, afunctional group having an unsaturated bonding such as CH₂ ═CH--, CH₂═CH--COO--, CH₂ ═CCH₃ --COO--, and ##STR1## or a hetero ring structurewith a distortion; B denotes a combining group combining thepolymerizable functional group and the liquid crystalline compound, forexample, bonding groups such as an alkyl chain (--(CH₂)_(n) --), anester bonding (--COO--), an ether bonding (--O--), and apolyethyleneglycol chain (--CH₂ CH₂ O--), and a combination thereof; andLC denotes the liquid crystalline compound. The combining group Bpreferably exhibits the liquid crystallinity when the polymerizableliquid crystalline material is mixed with the liquid crystal material.Accordingly, the combining group B has six or more bondings from thepolymerizable functional group A to the rigid portion of the liquidcrystalline material LC. The liquid crystalline material LC is acompound expressed by formula (2) below, a cholesterol ring, aderivative thereof, or the like.

    D-E-G                                                      (2)

G denotes a polar group which exhibits the dielectric constantanisotropy and the like of liquid crystal, for example, a benzene ringhaving a functional group such as --CN, --OCH₃, --Cl, --OCF₃, --OCCl₃,--H, and --R (R denotes an alkyl group), a cyclohexane ring, aparadiphenyl ring, and phenylcyclohexane ring. E denotes a functionalgroup combining D and G, for example, a single bonding, --CH₂ --, --CH₂CH₂ --, --O--, --C.tbd.C--, and --CH═CH--. Finally, D denotes afunctional group bonding with B, which influences the magnitude of thedielectric constant anisotropy and the refractive index anisotropy ofthe liquid crystal molecules, for example, a paraphenyl ring, a1,10-diphenyl ring, 1,4-cyclohexane ring, and 1,10-phenylcyclohexanering.

(Mixture ratio of the liquid crystal to the polymerizable material)

The mixture ratio by weight of the liquid crystal to the polymerizablematerial (including the curable resin and the polymerizable liquidcrystalline material) is preferably 50:50 to 97:3, more preferably 70:30to 90:10, though it depends on the size of the pixel. If the liquidcrystal material is less than 50%, the effect of the polymer wallincreases, which rises the driving voltage of the cell so greatly as tobecome impractical. If the liquid crystal material is more than 97%, thephysical strength of the polymer wall lowers, and thus a stableperformance is not obtainable. The percentage of the polymerizableliquid crystalline material in the total polymerizable material of theabove ratio may be 0.5% or more by weight.

(Method for driving the cell)

The fabricated cell can be driven by a simple matrix driving method oran active matrix driving method by the use of TFTs or MIMs. The drivingmethod is not specified in the present invention.

(Substrate material)

Any transparent solid body allowing visible light to be transmittedthrough may be used as the substrate material. Specifically, glass,quartz, plastic, or a polymer film may be used. Particularly, a plasticsubstrate is suitable because a roughened surface can be formed byembossing and the like. Also, two different types of materials may beused to form a cell having a pair of substrates made of differentmaterials. The pair of substrates made of the same material or differentmaterials may have different thicknesses.

Now, the present invention will be described by way of examples togetherwith comparative examples as follows.

EXAMPLE 1

Referring to FIG. 11, the transparent electrodes 3 and 6 made of ITO (amixture of indium oxide and tin oxide; 500 Å) were formed on the pair ofglass substrates 1 and 2 having a thickness of 1.1 mm, respectively. Theconvex portion 4 and the first wall 5 were formed on the substrate 1 atthe center of each pixel and surrounding the pixel, respectively, usinga resist material (OMR 83; manufactured by Tokyo Ohka Kogyo Co., Ltd.).A light shielding layer made of an Mo thin film was formed under theresist. The substrate 1 and the multilayer structure formed thereon arehereinafter collectively referred to as a first substrate.

AL 4552 (manufactured by Japan Synthetic Rubber Co., Ltd.) was appliedto the substrate 2 to form an alignment film 17 without rubbing. Thesubstrate 2 and the multilayer structure formed thereon are hereinaftercollectively referred to as a second substrate.

The first and second substrates are attached together with spacers of asize of 6 μm corresponding to a cell thickness interposed therebetweento form a cell.

A mixture of 0.1 g of R-684 (manufactured by Nippon Kayaku Co., Ltd.) asthe photocurable resin, 0.1 g of p-phenylstyrene as thephotopolymerization retarder, 0.06 g of a compound having formula (A)below, 3.74 g of ZLI-4792 (manufactured by Merck; containing 0.4% byweight of S-811) as the liquid crystal material, and 0.025 g of Irgacure651 as the photopolymerization initiator were injected into the cell.##STR2##

Thereafter, while the temperature was kept at 110° C. above thehomogeneously miscible temperature of the mixture and a voltage of aneffective voltage of 2.5 V, 60 Hz was applied between the transparentelectrodes 3 and 6, the cell was irradiated with ultraviolet light forfive minutes from the side of the first substrate 1 at the position of10 mW/cm² below a high-pressure mercury lamp, so as to cure the resin.Then, the cell was gradually cooled to 40° C. for five hours, and afterthe temperature was returned to room temperature (25° C.), the cell wasagain irradiated with ultraviolet light so as to cure the resincompletely.

The cell was observed at this stage by a polarizing microscope. As aresult, as shown in FIG. 2, it was found that the liquid crystal region8 surrounded by the polymer wall 7 was formed in the mono-domain statefor each pixel and liquid crystal molecules were alignedaxial-symmetrically around the portion 12 corresponding to the convexportion 4 made of the resist. Two polarizing plates having polarizingaxes crossing each other at right angles were fixed to the cell and thecell was rotated. As a result, the cell was observed as if theextinction pattern 11 was immobilized while only the polymer wall 7surrounding the pixel was rotating. This indicates that the liquidcrystal molecules are aligned axial-symmetrically over the entire liquidcrystal region 8.

Two polarizing plates having polarizing axes crossing each other atright angles were disposed on the opposite surfaces of the cell, so asto complete a liquid crystal display device.

The thus-fabricated liquid crystal display device was observed with thepolarizing microscope while being applied with a voltage. As a result,it was confirmed that no disclination line was produced even at the timeof voltage application and the entire pixel turned black.

The electro-optic characteristics and the evaluation of the roughness ofdisplay the thus-fabricated liquid crystal display device are shown inTable 1 below and FIG. 16. Table 1 also shows the results of ComparativeExample 1 and Comparative Example 2 to be described later. Theevaluation of the roughness of display obtained in Comparative Example 1is shown in FIG. 17. As for the electro-optic characteristics, twopolarizing plates having the polarizing axes parallel to each other wereshown as blank (transmittance 100%). In the item "inversion at grayscale level" in Table 1, mark ◯ indicates that no inversion occurred,mark indicates that inversion was easily observed, and mark indicatesthat inversion was weakly observed.

                  TABLE 1                                                         ______________________________________                                                             Compara- Compara-                                                   Example   tive     tive                                                       1         Example 1                                                                              Example 2                                       ______________________________________                                        Light transmittance                                                                        77          87       78                                          at no voltage                                                                 application (%)                                                               Inversion at gray                                                                          ◯                                                                             X        Δ                                     scale level                                                                   Roughness of No          No       Yes*                                        display                                                                       ______________________________________                                         *when observed at a wide angle at gray scale level.                      

As shown in FIGS. 16A to 16F and 17A to 17F, the liquid crystal displaydevice of Example 1 exhibits neither an inversion phenomenon as isobserved for a TN cell of Comparative Example 1, nor an increase in thetransmittance in the wide viewing direction at the time of voltagesaturation. Moreover, as shown in Table 1, no roughness of display wasobserved at the gray scale level.

Comparative Example 1

The pair of glass substrates 1 and 2 having the transparent electrodes 3and 6 made of ITO formed thereon were used as in Example 1. Alignmentfilms were formed on both substrates and rubbed. These substrates wereattached together so that the alignment directions of the alignmentfilms cross each other at right angles, with spacers of a size of 6 μmcorresponding to the cell thickness interposed therebetween, so as toform a cell.

The liquid crystal material, ZLI-4792 (manufactured by Merck; containing0.4% by weight of S-811) used in Example 1 was injected into the cell,and two polarizing plates were disposed on the outer surfaces of thecell so that polarizing axes thereof cross each other at right angles,so as to complete a liquid crystal display device.

The electro-optic characteristics and the evaluation of the roughness ofdisplay of the resultant liquid crystal display device are shown inTable 1 and FIGS. 17A to 17F.

EXAMPLE 2

In Example 2, a cell was fabricated in the same manner as in Example 1,except that in Example 2 the concave portion 15 was formed at the centerof each pixel as shown in FIG. 12, and the same mixture as that used inExample 1 was injected into a space between the pair of substrates.

The resultant cell was heated to a temperature higher than thehomogeneously miscible temperature of the mixture while a voltage of aneffective value of 2.5 V, 60 Hz was applied between the transparentelectrodes 3 and 6 of the cell. Then, the cell was gradually cooled soas to separate the liquid crystal. After the separation of the liquidcrystal, the application of the voltage was discontinued. After theliquid crystal phase almost expanded to the entire pixel, the cell wasirradiated with ultraviolet light, so as to cure the resin.

In the resultant liquid crystal display device, it was observed that theliquid crystal molecules were aligned axial-symmetrically around theconcave portion 15 in the liquid crystal region. No roughness of displaywas observed at the gray scale level.

EXAMPLE 3

In Example 3, a liquid crystal display device was fabricated in the samemanner as in Example 1, except that in Example 3 the convex portion 4was formed at the center of each pixel and the concave portion 15 wasformed around the convex portion 4.

In the resultant liquid crystal display device, it was observed that theliquid crystal molecules were aligned axial-symmetrically around theconvex portion 4 in the liquid crystal region. No roughness of displaywas observed at the gray scale level.

EXAMPLE 4

In Example 4, a cell was fabricated in the same manner as in Example 1,except that in Example 4 an alignment film 16 was formed on thesubstrate 1 covering the convex portion 4 and the first wall 5 by spincoating as shown in FIG. 5. The same mixture as that used in Example 1was injected in a space between the pair of substrates. The resin wascured in the same manner as that described in Example 2.

The phase separation of the mixture of this example at the gradualtemperature drop was examined, and it was confirmed that: The liquidcrystal phase appeared in the region having a larger cell thickness (theconcave portion 15) and expanded therefrom; the symmetry axis of theorientation of the liquid crystal molecules was located in the regionhaving the larger cell thickness; and a liquid crystal droplet was grownwhile the position of the axis for the axial-symmetric orientation ofthe liquid crystal molecules was intentionally controlled to correspondto the convex portion 4 at the center of the pixel. Such a dropletformed in the region having a larger cell thickness is shaped morespherical compared with a droplet formed in a region having a smallercell thickness. The spherical droplet is considered to have acomparatively small surface energy and thus is stable. Accordingly, theliquid crystal phase appears from the region having the largest cellthickness and the position of the symmetry axis of the orientation ofthe liquid crystal molecules is limited.

In the resultant liquid crystal display device, it was observed that theliquid crystal molecules were aligned axial-symmetrically around theconvex portion 4 in the liquid crystal region. No roughness of displaywas observed at the gray scale level.

EXAMPLE 5

In Example 5, a cell was fabricated in the same manner as in Example 1,except that in Example 5, as shown in FIG. 19, a rectangular pixel 13was divided into two and a first wall 21a and convex portions 21b wereformed on the substrate 1 using a black resist (CFPR-BK501S;manufactured by Tokyo Ohka Kogyo Co., Ltd.).

The thus-fabricated cell was observed with the polarizing microscope andit was found that two liquid crystal domains each in the mono-domainstate were formed in each pixel and that the liquid crystal molecules ineach domain were aligned axial-symmetrically around a portioncorresponding to the convex portion 21b as the symmetry axis.

In the resultant liquid crystal display device, it was observed that theliquid crystal molecules were aligned axial-symmetrically around theconvex portion 21a in the liquid crystal region. No roughness of displaywas observed at the gray scale level.

Comparative Example 2

In Comparative Example 2, a cell was fabricated in the same manner as inExample 1, except that in this example the center portion of the pixelis flat as shown in FIG. 20. The same mixture as that used in Example 1was injected in a space between the pair of substrates and cured asdescribed in Example 1.

The thus-fabricated cell was observed with the polarizing microscope andit was found that most liquid crystal regions had the axial-symmetricorientation. However, in some liquid crystal regions 8, the position ofa symmetry axis 18 was displaced as shown in FIG. 21A, while, in otherliquid crystal regions 8, no symmetry axis was formed as shown in FIG.21B. Significant roughness of the display was not observed especially atthe gray scale level at the time of voltage application.

EXAMPLE 6

In Example 6, a cell was fabricated in the same manner as in Example 1,except that in Example 6 an alignment film 16a having axial-symmetricorientation axes was formed on a substrate 1a as shown in FIG. 14A. Thealignment film 16a was formed in the following manner.

Referring to FIGS. 14B to 14D, after the formation of the first wall 5on the substrate 1a, a mixed material 22 containing two different typesof polymer materials (such as polyimide) was applied to the substrate 1acovering the first wall 5, dried to be phase-separated, and then baked.

The two types of polymer materials were phase-separatedaxial-symmetrically in each pixel on the substrate 1a, and thus thealignment film 16a having the axial-symmetric orientation axes wasobtained. A mixture containing the liquid crystal and the curable resinas described in Example 1 was injected into a space formed between thepair of substrates, and under the processing conditions as described inExample 1, a liquid crystal display device where liquid crystalmolecules were aligned axial-symmetrically was fabricated.

The thus-fabricated liquid crystal display device was observed with thepolarizing microscope and found that the liquid crystal molecules werealigned axial-symmetrically with the orientational pattern substantiallyidentical to the orientation axes of the alignment film 16a. Theroughness of display was hardly observed at the gray scale level.

EXAMPLE 7

In Example 7, the case where the convex portion formed at the center ofthe pixel is made of a material having the vertical alignment propertyso as to form stably orientation axes in axial-symmetric manner will bedescribed.

As shown in FIG. 29, a convex portion 52 was formed at the center of thepixel on a substrate 51 which includes a transparent electrode made ofITO (a mixture of indium oxide and tin oxide; thickness: 500 Å) formedon a glass substrate (thickness: 1.1 mm). The convex portion 52 was madeof a resist having the vertical alignment property (a resist produced byadding a curable material to JALS 204). A first wall 53 was formed usinga resist material (OMR 83; manufactured by Tokyo Ohka Kogyo Co., Ltd.)outside the pixel portion so as to enclose the convex portion 52. Alight shielding layer made of an Mo thin film was formed under theresist. The substrate 51 and the structure formed thereon arehereinafter called a first substrate.

AL 4552 (manufactured by Japan Synthetic Rubber Co., Ltd.) was appliedto another substrate 54 to form an alignment film 55 without rubbing.The substrate 2 and the film formed thereon are hereinafter collectivelycalled a second substrate.

The first and second substrates are attached together with spacers of asize of 5 μm corresponding to a cell thickness interposed therebetweenso as to form a cell. A mixture of 0.1 g of R-684 (manufactured byNippon Kayaku Co., Ltd.), 0.1 g of p-phenylstyrene, 0.06 g of a compoundhaving formula (A) above, 3.74 g of ZLI-4792 (manufactured by Merck;containing 0.4% by weight of S-811) as the liquid crystal material, and0.02 g of Irgacure 651 as the photopolymerization initiator was injectedinto the cell.

Thereafter, the temperature of the cell was kept at 110° C. Then, thecell was cooled to a room temperature, and heated again to between 50°C. and 60° C. while being applied with a voltage of an effective valueof 5 V, 60 Hz. At this temperature, the voltage was turned on and offrepeatedly so as to align the liquid crystal axial-symmetrically. Thecell was then gradually cooled to 30° C. for seven hours.

At the above state, the liquid crystal molecules in each pixel werealigned axial-symmetrically. This indicates that the convex portion ofExample 7 made of the material having the vertical alignment propertywas effective in improving the stability of the axial-symmetricorientation of the liquid crystal molecules. At this state, the cell wasirradiated with ultraviolet light for 20 minutes from the side of thefirst substrate at the position of 2 mW/cm² below a high-pressuremercury lamp, so as to cure the resin.

Then, the cell may be cooled to a temperature less than the roomtemperature to facilitate the separation of the liquid crystal from anunreacted portion of the photocurable resin and may be irradiated againwith ultraviolet light.

The thus-fabricated liquid crystal cell was observed with the polarizingmicroscope. As a result, as shown in FIG. 30, it was found that theliquid crystal molecules were aligned axial-symmetrically around theisland of the resist (the convex portion made of the material having thevertical alignment property) in the mono-domain state for each pixel.This axial-symmetric orientation was observed in almost all liquidcrystal regions.

Two polarizing plates having polarizing axes crossing each other atright angles were disposed on the opposite outer surfaces of the cell,so as to complete a liquid crystal display device surrounded by thepolymer wall. The above liquid crystal cell was observed with thepolarizing microscope with a voltage applied thereto. As a result, itwas found that no disclination line arose even at the time of voltageapplication and the entire pixel turned black.

The electro-optic characteristics and the evaluation of the roughness ofthe fabricated liquid crystal cell are shown in Table 2 below. It wasfound from Table 2 that the liquid crystal cell of Example 7 exhibitedneither an inversion phenomenon as was observed in the TN cell nor anincrease in the transmittance in a wide viewing direction at the voltagesaturation. In the measurement, the two polarizing plates having thepolarizing axes parallel to each other were shown as blank(transmittance 100%). No roughness of display was observed at the grayscale level. In the item "inversion at gray scale level" in Table 2, amark ◯ indicates that no inversion occurred.

                  TABLE 2                                                         ______________________________________                                                    Example  Example  Example                                                     7        8        9                                               ______________________________________                                        Light transmittance                                                                         78         79       77                                          at no voltage                                                                 application (%)                                                               Inversion at gray                                                                           ◯                                                                            ◯                                                                          ◯                               scale level                                                                   Roughness of display                                                                        No         No       No                                          ______________________________________                                    

EXAMPLE 8

Example 8, which shows the case where a high-temperature irradiation andgradual cooling method is adopted for the fabrication of the liquidcrystal cell of Example 7, will be described.

A mixture containing the liquid crystal material and the photocurableresin material was injected into a space between the pair of substratesas described in Example 7. The cell was heated to 110° C. which is thehomogeneously miscible temperature of the liquid crystal. Thereafter,while keeping the temperature of 110° C., a voltage having an effectivevalue of 2.5 V, 60 Hz was applied between the transparent electrodes.Simultaneously, the cell was irradiated with ultraviolet light for fourminutes from the side of the first substrate at the position of 10mW/cm² below a high-pressure mercury lamp, so as to cure the resin. Atthe temperature of 50° C. to 60° C. the voltage was turned on (a voltageat which liquid crystal is driven or higher) and off repeatedly. Thecell was then gradually cooled to 30° C. for two hours. Thereafter, thetemperature was returned to room temperature (25° C.) and the cell wasagain irradiated with ultraviolet light by use of the same ultravioletirradiation apparatus, so as to complete the curing of the curableresin.

The electro-optic characteristics and the evaluation of roughness of thethus-fabricated liquid crystal cell are shown in Table 2 above.

EXAMPLE 9

In Example 9, the case where two convex islands having the verticalalignment property are formed at the center of the pixel on the twosubstrates will be described.

Referring to FIG. 31, a convex portion 57 having the vertical alignmentproperty was formed on one of the substrates as the first substrate ofExample 7. A convex portion 58 was formed on an alignment film of theother substrate at a position corresponding to the convex portion 57.Thus, a liquid crystal cell was fabricated as in Example 7. In theresultant liquid crystal cell, i.e., the liquid crystal display device,the liquid crystal molecules were stably aligned axial-symmetrically,and no roughness of display was observed at the gray scale level.

The electro-optic characteristics and the evaluation of roughness of thethus-fabricated liquid crystal cell are shown in Table 2 above.

In Examples 7 to 9, the liquid crystal molecules are aligned in eachpixel axial-symmetrically around the center portion of the pixel as thecenter of the symmetry. Since the liquid crystal molecules are alignedin all directions, the trouble of the lowering of the contrast dependingon the viewing direction arising in the conventional liquid crystaldisplay devices can be improved. Further, since an island having thevertical alignment property is formed at the center of each pixel, theaxial symmetric orientation of the liquid crystal molecules isstabilized and the position of the axis of the axial-symmetricorientation in the pixel can be definitely determined. This makes itpossible to reduce the roughness of display which is observed when theviewing angle is changed. Thus, a liquid crystal device with a wideviewing angle providing uniform and high-contrast images can berealized.

In Examples 7 to 9, the convex portion having the vertical alignmentproperty was formed at the center of each pixel. A concave portion maybe formed in place of the convex portion, or both the convex and concaveportions may be formed in combination.

EXAMPLE 10

In Example 10, active driving elements are formed on the substrate onwhich the convex or concave portion for obtaining the stableaxial-symmetric orientation axes is formed for each pixel. A colorfilter substrate as used as the counter substrate. At the phaseseparation, a source signal, a gate signal, and a timing voltage for acounter voltage are applied.

As shown in FIGS. 27 and 28, Cr was deposited on a glass substrate 46 byvapor deposition and patterned to form gate lines 44. Then, amorphoussilicon for a gate insulating film was deposited by a plasma CVDapparatus and polycrystallized by laser annealing. The polycrystallinesilicon was patterned into islands to form semiconductor layers. P-dopedamorphous silicon was then deposited on the semiconductor layers byplasma CVD and patterned so as to cover the semiconductor layers. ITOwas then deposited and patterned to form pixel electrodes. Thereafter,Cr and Al were deposited and patterned into a predetermined shape. TheseAl, Cr, and P-doped amorphous silicon were etched in this order to formsource and drain electrodes. Silicon nitride was deposited by plasma CVDto form a protection film. Finally, the protection film was etched atthe periphery of the substrate to form terminal electrodes, so as tocomplete the TFT substrate. A resist material (OMR 83) was applied tothe TFT substrate by spin coating. A light shielding mask covering thepixel electrode area and exposing the area of a diameter of 10 μm fromthe center of each pixel was superposed on the resist-coated substrate,and the substrate was irradiated with ultraviolet light from the side ofthe light shielding mask so as to etch uncured portions. Thus, walls 47were formed in areas other than the pixel electrodes and convex portions48 having a diameter of 10 m were formed in a pattern of islands made ofthe resist at the centers of the pixel electrodes.

As described above, the convex (or concave) portions of the pattern ofislands are formed on the side of the first substrate facing the liquidcrystal regions. Thus, the liquid crystal molecules can be alignedaxial-symmetrically in each liquid crystal region using the convexportion or the vicinity thereof as the vertical axis.

As for the second substrate, as shown in FIGS. 24 and 25, lightshielding films 32 were formed at gaps between the regions on thecounter substrate corresponding to the pixels formed on the firstsubstrate. Then, resin layers were formed on the above regions so as toform color filter portions 33 which were colored with R, G, and B inorder. The resultant second substrate was applied with a resist material(OMR 83) by spin coating. A light shielding mask exposing the areasother than the color filter portions 33 was then superposed on thecoated substrate. The substrate was then irradiated with ultravioletlight from the side of the light shielding mask, and uncured portionswere etched. Thus, the areas other than the color filter portions 33were filled with resist resin 34 to smooth the surface. In other words,the color filter portions 33 were formed on a substrate 31 and theremaining areas other than the color filter portions 33 were filled withthe resist resin 34 so as to smooth the surface.

As described above, in the liquid crystal display device where theliquid crystal molecules are aligned axial-symmetrically in each pixel,the surface of at least one substrate (the second substrate in Example10) is smoothed.

The thus-fabricated first and second substrates were attached togetherwith spacers of a size of 6 μm interposed therebetween as the cellthickness, so as to form a cell. Predetermined positions on the firstand second substrates are not covered with the resist so as to form ITOelectrodes for electrical connection. They are electrically connectedwith a carbon paste (TU-100-5S, manufactured by Asahi Kagaku). Themixture containing the liquid crystal material and the curable resinmaterial described in Example 1 was injected into the cell. The cell washeated to 110° C., and while this temperature was kept, signal voltagesshown in FIG. 32 were applied to the source electrode, the gateelectrode, and the counter electrode using the potential at the counterelectrode as the reference: a rectangular wave voltage of 60 Hz, ±2.5 V,and a 1/2 duty was applied to the source electrode; and a rectangularwave voltage of 120 Hz, +10 V for 60 μs and -16 V for the other of thecycle was applied to the gate electrode in synchronization with thesource voltage. Simultaneously, the cell was irradiated with ultravioletlight of an intensity of 10 mW/cm² from a high-pressure mercury lampfrom the side of the first substrate, so as to cure the curable resin.Thereafter, the cell was gradually cooled to 40° C. for five hours.After the temperature was returned to room temperature (25° C.), thecell was again irradiated with ultraviolet light by use of the sameirradiation apparatus, so as to complete the curing of the curableresin.

The thus-fabricated cell was observed with the polarizing microscope. Asa result, as shown in FIG. 2, it was found that the liquid crystalmolecules were aligned axial-symmetrically around the island of theresist in the mono-domain state for each pixel. This axial-symmetricalignment was realized in almost all liquid crystal regions. This wasjudged from the fact that the Schlierene pattern in the liquid crystalregion was observed immobilized while only the polymer wall 7surrounding the pixel was rotating.

Two polarizing plates having polarizing axes crossing each other atright angles were disposed on the opposite outer surfaces of the cell,so as to complete a liquid crystal display cell surrounded by thepolymer wall. The above cell was observed with the polarizing microscopewith a voltage applied thereto. As a result, it was found that nodisclination line arose even at the time of voltage application and theentire pixel turned black. The liquid crystal cell exhibited neither aninversion phenomenon, as was observed in the TN cell (ComparativeExample 1), nor an increase in the transmittance in the wide viewingangle at the time of voltage saturation. In the measurement, the twopolarizing plates having the polarizing axes parallel to each other wereshown as blank (transmittance 100%). No roughness of display wasobserved at the gray scale level.

Conventionally, concaves are present between adjacent color filterportions. At the phase separation of the liquid crystal from the curableresin, the liquid crystal tends to appear in portions having a largercell thickness. Accordingly, since liquid crystal droplets tend to beformed at the concaves between the color filter portions, theaxial-symmetric orientation of the liquid crystal molecules is disturbedby the concaves. This trouble can be overcome by filling the concaveswith the resist material to smooth the surface of the color filtersubstrate. By this smoothing treatment, the liquid crystal can beseparated only at the convex portion on the opposing substrate. In thecase of active driving elements, many steps are formed by the multilayerstructure of the active driving elements and the wirings thereof.Therefore, the axial-symmetric orientation of the liquid crystalmolecules in the droplet is disturbed. This trouble can be overcome byfilling concaves formed by these steps to smooth the surface.

Also, the signal voltage for driving the gate of the active drivingelement is synchronous with the signal voltage for driving the sourcethereof, the pulse width of the former is a half or less of the cycle ofthe latter, and the resin is cured while the voltage is applied.Accordingly, the potential difference between the pixel electrode andthe gate line formed on the same substrate is decreased, and such atrouble that the axial-symmetric orientation of the liquid crystalmolecules is disturbed due to the potential at the gate line can beovercome.

As described above, in the liquid crystal display device of thisexample, the position of the axis of the axial-symmetric orientation ofthe liquid crystal molecules can be definitely determined, the roughnessof display observed when the viewing angle is changed can be minimized,and a liquid crystal device with a wide viewing angle providing uniformand high-contrast images can be realized.

Thus, according to the present invention, liquid crystal molecules ineach liquid crystal region are aligned axial-symmetrically. Accordingly,the variation in the contrast observed in conventional liquid crystaldisplay devices can be minimized. Since the position of the symmetryaxis in each pixel can be controlled and the symmetry axis can bevertical to the substrates, the roughness of display observed when theviewing angle is changed can be reduced. Thus, a liquid crystal displaydevice with a wide viewing angle providing uniform and high-contrastimages can be realized. Moreover, the disclination line is formedoutside the pixel or made less visible. This makes it possible toimprove the display quality.

Further, the convex or concave portion, as an island having the verticalalignment property, is formed at the center of each pixel. Accordingly,the axial symmetry is stabilized, and the position of the axis for theaxial-symmetric orientation in each pixel can be definitely determined.This serves to reduce the roughness of display observed when the viewingangle is changed. Also, a liquid crystal display device with a wideviewing angle providing uniform and high-contrast images can berealized.

Moreover, by smoothing the surface of the electrode substrate facing theother substrate, the orientation of the liquid crystal droplet isprevented from being disturbed by concaves on he substrate. For example,when a color filter is formed on the electrode substrate, concavesbetween color filter portions are filled with a resin to smooth thesurface. Thus, the liquid crystal phase appears only at the concave orconvex portions formed on the other substrate facing the color filter.As another example, when active driving elements are formed on theelectrode substrate, many steps are formed on the surface by themultilayer structure of the active driving elements and the wiringsthereof. In this case, also, the steps are filled with a resin to smooththe surface. Thus, the liquid crystal phase appears only at the concaveor convex portion formed at the center of each pixel. Accordingly, theposition of the axis for the axial-symmetric orientation in each pixelcan be definitely determined, the roughness of display observed when theviewing angle is changed can be minimized, and a liquid crystal devicewith a wide viewing angle providing uniform and high-contrast images canbe realized.

Furthermore, the signal voltage for driving the gate of the activedriving element is synchronous with the signal voltage for driving thesource thereof. The cycle of the former is a half of the cycle of thelatter, and the pulse width of the former is a half or less of the cycleof the latter. The resin is cured while the above voltages are applied.Since the gate signal line is arranged in the vicinity of each pixelelectrode, the potential at the gate signal voltage affects thepotential in the vicinity of the pixel electrode. The potential in thevicinity of the pixel electrode is less affected by the gate signalvoltage if the duration of the signal voltage applied to the gateelectrode is shorter than the duration when the source driving signalvoltage is applied to the pixel electrode. Accordingly, the potentialdifference between the pixel electrode and the gate line formed on thesame substrate is decreased, and the trouble with the axial-symmetricorientation possibly being disturbed due to the potential at the gateline can be overcome. Accordingly, the position of the axis for theaxial-symmetric orientation of the liquid crystal in each pixel can bedefinitely determined, the roughness of display observed when theviewing angle is changed can be minimized, and a liquid crystal devicewith a wide viewing angle providing uniform and high-contrast images canbe realized.

EXAMPLE 11, Comparative Examples 3 and 4

In Example 11, a method for simply forming a concave portion on a colorfilter portion for controlling the position of the symmetry axis for thealignment of liquid crystal molecules will be described.

Referring to FIGS. 33A to 33E, the method for fabricating a color filtersubstrate 60 of this example will be described.

First, a color filter 63 is formed on a substrate 62 as shown in FIG.33A. The color filter 63 is composed of color filter portions 63a, 63b,and 63c corresponding to red (R), green (G), and blue (B), respectively.The color filter portions 63a, 63b, and 63c are formed so as tocorrespond to the respective pixels. Such a color filter 63 may beformed by electrodeposition, film adhesion, printing, color-resistformation, or the like, though not specified in the present invention.

Then, as shown in FIG. 33B, a resist 64 is applied to the substrate 62,covering the color filter portions 63a, 63b, and 63c. As shown in FIG.33C, the resist 64 is exposed to light and developed so that convexwalls 65 made of the resist can be formed in the portions outside thepixel portions (portions other than the color filter portions). It isimportant that the convex walls 65 formed on the substrate 62 should behigher than the color filter portions 63a, 63b, and 63c so as to extrudefarther toward the liquid crystal layer.

Thereafter, as shown in FIG. 33D, a thin overcoat layer 66 is formedover the substrate 62 having the convex walls 65. Due to the surfacetension (meniscus) of the liquid overcoat material and the extrusion ofthe convex walls 65, concave (conical) portions are formed on therespective color filter portions 63a, 63b, and 63c. A transparentelectrode 67 is formed over the overcoat layer 66 formed on thesubstrate 62, as shown in FIG. 33E. An insulating layer and/or analignment film may be formed on the transparent electrode 67, ifrequired. Thus, the color filter substrate 60 is fabricated.

(Overcoat material)

A General overcoat material may be used as the material for forming theconcave portions. In the present invention, the overcoat layer iscovered with the transparent electrode and eternally remains in theliquid crystal cell. Accordingly, it is preferable to use polyimide,epoxyacrylate, and the like which have excellent heat resistanceproperties.

(The number of domains in one pixel)

The number of domains in each pixel is preferably as small as possible.If a number of domains exist in one pixel, a disclination line arises ateach boundary of domains, causing degradation in the black level of thedisplay. It is preferable, therefore, that the pixel portion is coveredby a single domain where liquid crystal molecules are alignedaxial-symmetrically. With this arrangement, since the disclination lineis formed outside the domain at the time of voltage application, thedisclination line seldom intrudes inside the pixel portion.

In the case of fabricating a color liquid crystal display device havingthe rectangular pixel 13 as shown in FIG. 3 according to the method ofExample 11, the liquid crystal region 8 may have two or more liquidcrystal domains 14a and 14b each having liquid crystal molecules alignedaxial-symmetrically. In this case, two color filter portions are formedin correspondence with the two liquid crystal domains 14a and 14b in thepixel 13. Then, in accordance with the steps shown in FIGS. 33A to 33E,the concave portions for controlling the position of the symmetry axisfor the alignment of the liquid crystal can be formed for the two liquidcrystal domains 14a and 14b in the pixel 13. The convex walls 65 may bemade of a material having a light shielding property so as to serve as ablack mask (BM).

(Substrate material)

The substrate 62 may be made of any transparent solid body allowingvisible light to transmit therethrough. Specifically, glass, quartz,plastic, and the like may be used.

Now, the method for fabricating the color filter substrate 60 of Example11 will de described in detail with reference to FIGS. 33A to 33E.

The color filter portions 63a, 63b, and 63c corresponding to R, G, and Bare formed for respective pixels on the glass substrate 62 (thickness:1.1 mm) by use of a color resist. The resist 64 (V259PA, manufactured byNippon Steel Chemical Co., Ltd.) is then applied to the substrate 62,covering the color filter portions 63a, 63b, and 63c. The resist 64 isexposed to light and developed so that the convex portions 65 made ofthe resist are formed outside the pixels. The convex portions 65 areformed so as to extrude from the pixel portions by about 1 μm. The thinovercoat layer 66 (V259, manufactured by Nippon Steel Chemical Co.,Ltd.) is formed over the substrate 62 having the convex walls 65 so asto form conical concave portions on the pixel portions. The transparentelectrode 67 made of ITO (a mixture of indium oxide and tin oxide)having a thickness of 50 nm and an insulating film (SiO₂) are formedover the substrate 62 in this order.

As Comparative Example 3, a color filter substrate 70 shown in FIG. 34was fabricated as follows. The color filter portions 63 were formed onthe glass substrate 62 as in the case of the color filter substrate 60in Example 11. Then, the thick overcoat layer 66 was formed over thesubstrate 62, covering the color filter portions 63. The surface of theovercoat layer 66 was polished so as to obtain the flat surface facingthe liquid crystal. The transparent electrode 67 was formed over theovercoat layer 66 so as to complete the color filter substrate 70.

As Comparative Example 4, a color filter substrate 80 shown in FIG. 35was fabricated as follows. The color filter substrate 80 has concaveportions between the adjacent color filter portions 63.

First, as in the case of the color filter substrate 60, the color filterportions 63 were formed on the glass substrate 62. Then, the thinovercoat layer 66 was formed over the substrate having the color filterportions 63 without filling the spaces between the adjacent color filterportions 63 with a resist. Since the overcoat layer 66 is thin, concaveportions were formed between the color filter portions 63. Thetransparent electrode 67 was formed over the overcoat layer 66 so as tocomplete the color filter substrate 80.

On the other hand, a substrate having TFTs (TFT substrate) was preparedand a resist wall made of a resist material (OMR 83, manufactured byTokyo Ohka Kogyo Co., Ltd.) was formed around each pixel on the TFTsubstrate. Beads for realizing a uniform cell thickness were included inthe resist wall in such a manner that these beads were not exposedoutside the resist wall.

Liquid crystal cells of Example 11 and Comparative Examples 3 and 4 werefabricated using the color filter substrates 60, 70, and 80 and the TFTsubstrate described above, respectively.

In order to obtain a mixture of an ultraviolet-curable resin and liquidcrystal, 0.1 g of R-684 (manufactured by Nippon Kayaku Co., Ltd.), 0.1 gof p-phenylstyrene, 0.06 g of a compound having formula (A) above, 3.74g of ZLI-4792 (manufactured by Merck; containing 0.4% by weight ofS-811) as the liquid crystal material, and 0.02 g of Irgacure 651 as thephotopolymerization initiator were mixed. The resultant mixture wasinjected into the cell.

The cell was kept at 100° C. so as to maintain the miscible state of themixture. Then, the cell was cooled to cause the phase separation of themixture. The cell was heated again after the phase-separated liquidcrystal phase had expanded to the entire pixel. A voltage of aneffective value of 5 V, 60 Hz was applied between electrodes of the cellwhen the liquid crystal region had expanded to about one-fourth of thesize of the pixel. The voltage was then gradually decreased. As aresult, the liquid crystal molecules in the liquid crystal region werealigned axial-symmetrically.

FIGS. 36A to 36C show how the liquid crystal phase is separated from thecurable resin in Example 11 and Comparative Examples 3 and 4,respectively. The liquid crystal region tends to be formed at a portionhaving a large cell thickness. Accordingly, in Example 11, the liquidcrystal region is formed at the center of the pixel as shown in FIG.36A. On the other hand, in Comparative Example 3, the position where theliquid crystal region is formed is not fixed but varies among pixels asshown in FIG. 36B. In Comparative Example 4, the liquid crystal regiontends to be formed outside the pixel partially extending inside thepixel as shown in FIG. 36C.

Thereafter, the cell was cooled to room temperature, and was irradiatedwith ultraviolet light of an intensity of 2 mW/cm² from a high-pressuremercury lamp from the side of the TFT substrate for 30 minutes, so as tocure the curable resin.

FIGS. 37A to 37C show the results of the cell viewed with the polarizingmicroscope. In Example 11, the position of the symmetry axis for thealignment of liquid crystal molecules are at the center of each pixel asshown in FIG. 37A for all the pixels. In Comparative Example 3, thesymmetry axis for the alignment of liquid crystal molecules was greatlydisplaced as shown in FIG. 37B for several percent of pixels. As aresult, in Example 11, no roughness of display was observed and a gooddisplay quality was obtained. In Comparative Example 3, however, theroughness of display was observed at the gray scale level and at a lowviewing angle. In Comparative Example 4, since liquid crystal moleculeswere aligned axial-symmetrically in only about 30% of pixels, a badlyroughened display was observed.

According to this example, a liquid crystal display device is providedwith a color filter having concave portions each corresponding to apixel. The liquid crystal molecules are aligned axial-symmetricallyhaving the center portion of each pixel as the symmetry axis. Thus, theposition of the axis for the axial-symmetric orientation of the liquidcrystal molecules in each pixel can be definitely determined, theroughness of display observed when the viewing angle is changed can beminimized, and a liquid crystal device with a wide viewing angleproviding uniform and high-contrast images can be realized. Moreover,the color filter portions according to the present invention can befabricated in the same process as that for normal color filter portions.This provides a good cost performance.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A liquid crystal device comprising a pair ofelectrode substrates opposing each other, a polymer wall, and a liquidcrystal region surrounded by the polymer wall, the polymer wall and theliquid crystal region being sandwiched by the pair of electrodesubstrates,wherein at least one of a concave portion and a convexportion is formed on a surface of at least one of the pair of electrodesubstrates facing the liquid crystal region, and liquid crystalmolecules are oriented in the liquid crystal region axial-symmetricallyaround the vicinity of the at least one of the concave portion and theconvex portion as an axis vertical to the electrode substrates, andwherein a first wall is formed on a surface of at least one of the pairof substrates facing the liquid crystal region so as to surround theliquid crystal region or the liquid crystal domain, and a height H ofthe first wall and a height h of the convex portion have a relationshipof H>h, and further wherein, the polymer wall is formed on the firstwall.
 2. A liquid crystal device according to claim 1, wherein at leastone of the concave portion or the convex portion are made of a filmhaving a vertical alignment property or a horizontal alignment property.3. A liquid crystal device according to claim 1, wherein the liquidcrystal region is composed of a plurality of liquid crystal domainsdividing a pixel, and the polymer wall is formed at the periphery ofeach of the plurality of liquid crystal domains.
 4. A liquid crystaldevice according to claim 3, wherein colored additive is included in thepolymer wall.
 5. A liquid crystal device according to claim 1, whereinconcaves and convexes are formed axial-symmetrically or continuouslyaround the vicinity of a symmetry axis for the orientation of the liquidcrystal molecules.
 6. A liquid crystal device according to claim 1,wherein a region where the distance between the electrodes of the pairof electrode substrates is different from the distance in other regionsexists in the vicinity of the symmetry axis for the orientation of theliquid crystal molecules.
 7. A liquid crystal cell according to claim 1,wherein the at least one of the electrode substrates has a color filter,the color filter including a plurality of color filter portionscorresponding to a plurality of pixels and the concave portion is formedon a surface of each of the color filter portions facing the liquidcrystal region.
 8. A liquid crystal cell according to claim 7, whereinthe at least one of the electrode substrates includes convex wallsformed between the plurality of color filter portions and an overcoatlayer covering the plurality of color filter portions and the convexwalls.
 9. A liquid crystal cell according to claim 8, wherein the convexwalls have a light shielding property.
 10. A liquid crystal devicecomprising a pair of electrode substrates opposing each other, a polymerwall, and a liquid crystal region surrounded by the polymer wall, thepolymer wall and the liquid crystal region being sandwiched by the pairof electrode substrates,wherein at least one of a concave portion and aconvex portion is formed on a surface of at least one of the pair ofelectrode substrates facing the liquid crystal region, and liquidcrystal molecules are oriented in the liquid crystal regionaxial-symmetrically around the vicinity of the at least one of theconcave portion and the convex portion as an axis vertical to theelectrode substrates, and a smooth resin portion is formed on a surfaceof one or both of the pair of electrode substrates facing the liquidcrystal region, and wherein a first wall is formed on a surface of atleast one of the pair of substrates facing the liquid crystal region soas to surround the liquid crystal region or the liquid crystal domain,and a height H of the first wall and a height h of the convex portionhave a relationship of H>h, and further wherein, the polymer wall isformed on the first wall.
 11. A liquid crystal device according to claim10, wherein a color filter is formed on at least one of the pair ofelectrode substrates, and concaves between color filter portions of thecolor filter corresponding to the liquid crystal regions are filled witha resin forming the resin portions and smoothed.
 12. A liquid crystaldevice according to claim 10, wherein active driving elements fordriving the liquid crystal by applying a driving voltage to electrodesof the electrode substrates are formed on at least one of the pair ofelectrode substrates, and the active driving elements and wiringsthereof are covered with a resin forming the resin portions andsmoothed.
 13. A liquid crystal device according to claim 10, wherein theat least one of the concave portion and the convex portion are made of afilm having a vertical alignment property or a horizontal alignmentproperty.
 14. A liquid crystal device according to claim 10, wherein theliquid crystal region is composed of a plurality of liquid crystaldomains dividing a pixel, and the polymer wall is formed at theperiphery of each of the plurality of liquid crystal domains.
 15. Aliquid crystal device according to claim 14, wherein a colored additiveis included in the poller wall.
 16. A liquid crystal device according toclaim 10, wherein concaves and convexes are formed axial-symmetricallyor continuously around the vicinity of a symmetry axis for theorientation of the liquid crystal molecules.
 17. A liquid crystal deviceaccording to claim 10, wherein a region where the distance between theelectrodes of the pair of electrode substrates is different from thedistance in other regions exists in the vicinity of the symmetry axisfor the orientation of the liquid crystal molecules.
 18. A liquidcrystal device comprising a pair of electrode substrates opposing eachother, a polymer wall, and a liquid crystal region surrounded by thepolymer wall, the polymer wall and the liquid crystal region beingsandwiched by the pair of electrode substrates,wherein an alignment filmhaving axial-symmetric orientation axes is formed on a surface of atleast one of the pair of electrode substrates facing the liquid crystalregion, and wherein a first wall is formed on a surface of at least oneof the pair of substrates facing the liquid crystal region so as tosurround the liquid crystal region or the liquid crystal domain, andwherein the polymer wall is formed on the first wall, and furtherwherein liquid crystal molecules in the liquid crystal region areoriented axial-symmetrically around at least one of the axial-symmetricorientation axes.
 19. A method for fabricating a liquid crystal deviceincluding a pair of electrode substrates opposing each other, a polymerwall, and a liquid crystal region surrounded by the polymer wall, thepolymer wall and the liquid crystal region being sandwiched by the pairof electrode substrates, at least one of the pair of electrodesubstrates being fabricated by a method comprising the steps of:forminga plurality of color filter portions on a surface of the substrate;forming convex walls between the color filter portions; forming concaveportions on the surface of the plurality of color filter portions facingthe liquid crystal region by forming an overcoat layer covering theplurality of color filter portions and the convex walls.
 20. A methodaccording to claim 19, wherein the step of forming the concave portionscomprises the steps of:applying a resist covering the plurality of colorfilter portions; and forming the convex walls between the plurality ofcolor filter portions by exposing the resist to light and developing.